1911 Encyclopædia Britannica/Stone-fly

STONE-FLY, the name given to medium-sized, neuropterous insects of the family Perlidae with long flexible antennae, wide thoracic sterna and with the wings resembling, as regards size, shape and the fan-like folding of the posterior pair, those typical of the Orthoptera except that the anterior pair is membranous and not coriaceous. The immature forms, which are aquatic, carnivorous and active, are very like the adults except in the absence of wings and in their method of respiration, which is either cutaneous or effected by means of variously placed integumental tufts richly supplied with tracheae. By some authors the Perlidae are regarded as a special order, Plecoptera; by others as a sub-order of an order Platyptera, which contains the Termitidae and some other insects as well.